(1) Field of the Invention
The invention relates to a skid-type landing gear for a helicopter and a method for operating such a skid-type landing gear for a helicopter.
(2) Description of Related Art
The helicopter Bell 209 was equipped with a retractable skid-type landing gear.
U.S. Pat. No. 4,270,711 discloses a helicopter skid-type landing gear assembly including a pair of crosstubes having a pair of struts connected at the outboard ends thereof. A first of the crosstubes is connected to the helicopter fuselage at a pair of laterally spaced points. The second of the crosstubes is joined by a pivot connection to a structural bridge positioned above the second crosstube. The structural bridge is connected at its outer ends to the fuselage main beams. The structural bridge connected to the second crosstube permits the helicopter fuselage to pivot about a fore-aft axis thereof to lower the natural roll frequency of the helicopter airframe and therefore increase the margin of stability to prevent ground resonance.
EP 0564325 A1 relates to a retractable landing gear for a helicopter including a damping leg mounted so as to pivot, as well as an associated operating jack. The leg is produced in two elements which are articulated together around a shaft parallel to the axis of pivoting of the leg and are linked by a damper, the lower element forming a bell crank, and the upper element forming a panel whose free end is linked to an operating jack which is a damping jack with a force threshold, the said damping jack serving to apply the predetermined torque keeping the leg in its position during a normal landing, while allowing this leg to be retracted with a controlled force in the event of a crash landing.
Skid-type landing gears of helicopters according to the state of the art contribute considerably to the total air drag of a helicopter. During fast forward flight of a helicopter about 20% of the total air drag is contributed by the skid-type landing gears. An important amount of fuel has to be consumed during missions with a high cruising share to overcome this air drag with this extra amount of fuel adding to the costs of the mission and adding to the weight of the helicopter thus limiting the operational range of the helicopter.